Validate IP address with regular expressions and C#

[PsychoCoder]

I was doing some work for someone and needed to validate an IP address. Now you could use IPAddress.TryPa rse but it allows values like 0.0.0.0, so I used regular expressions and it worked much better.

/// <summary>
/// method to validate an IP address
/// using regular expressions. The pattern
/// being used will validate an ip address
/// with the range of 1.0.0.0 to 255.255.255.255
/// </summary>
/// <param name="addr">Address to validate</param>
/// <returns></returns>
public bool IsValidIP(string addr)
{
    //create our match pattern
    string pattern = @"^([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(\.
    ([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}$";
    //create our Regular Expression object
    Regex check = new Regex(pattern);
    //boolean variable to hold the status
    bool valid = false;
    //check to make sure an ip address was provided
    if (addr == "")
    {
        //no address provided so return false
        valid = false;
    }
    else
    {
        //address provided so use the IsMatch Method
        //of the Regular Expression object
        valid = check.IsMatch(addr, 0);
    }
    //return the results
    return valid;
}

Happy Coding!

[!NoItAll]

Ok - I think using TryParse and checking for 0.0.0.0 would be fine too. While the Regex for IPv4 is fairly straight-forward, I think applying this to IPv6 would require an indecipherable regex (e.g. unmaintainable code). Using TryParse creates a much more supportable code base IMHO.

[TomasRiker]

I just wrote an article about matching IP addresses with regular expressions. It also has a regex for IPv6 addresses, if you are interested (pretty simple though thanks to hex digits ;)).